A detailed study will be made of the release of LH, FSH and prolactin in the female rat at the time of vaginal opening, first ovulation and initiation of estrous cycles in order to clarify the sequence of events in relation to the stimulatory feedback of estrogen. Of particular interest is the question of whether the changes in gonadotropin release at puberty result from activation of mechanisms stimulating LRF release, or from changes in the responsiveness of the pituitary gland to a relatively constant LRF stimulus. Comparisons will be made of gonadotropin levels measured by radioimmunoassay, and the factors which determine them at natural puberty, 7-9 days earlier, and in conjunction with estrogen-induced precocious puberty.